1. Field of the Invention
The present invention relates to a recording tape cartridge which rotatably accommodates a reel on which a recording tape, such as a magnetic tape or the like, is wound.
2. Description of the Related Art
Recording tapes such as magnetic tapes and the like are used as external recording media for computers and the like. Little space is required to accommodate such a recording tape at the time of storage thereof, and a large amount of information can be recorded thereon. A so-called single-reel recording tape cartridge is used in which a single reel, on which the recording tape is wound, is rotatably accommodated within a case. Such a recording tape cartridge is equipped with a braking means so that the reel does not rotate within the case when the recording tape cartridge is not in use. (See, for example, Japanese Patent Application Laid-Open (JP-A) No. 63-251983.) A recording tape cartridge equipped with such a braking means will be described with reference to FIG. 11.
In a recording tape cartridge 200 illustrated in FIG. 11, a single reel 204 is accommodated within a case 202. The case 202 has a gear opening 206 provided at the central portion of a floor plate 202A, and a rotation restricting rib 208 projecting downwardly from a ceiling plate 202B.
The reel 204 has a reel hub 210 which is formed in the shape of a hollow cylinder having a bottom, and around whose outer peripheral portion a recording tape is wound. A reel gear 214, which can mesh with a driving gear 212A formed at a rotating shaft 212 of a drive device, is formed in an annular form at the bottom surface (the outer side) of a bottom portion 210A of the reel hub 210. On the other hand, an engaging gear 216 is formed in an annular form at the top surface (the inner side) of the bottom portion 210A. A through hole 218 is formed in the axially central portion of the bottom portion 210A. An annular reel plate 219, which is formed of a magnetic material and which has, in the axially central portion thereof, a through hole substantially corresponding to the through hole 218, is fixed to the radial direction inner side of the reel gear 214 at the bottom surface of the bottom portion 210A.
A disc-shaped braking member 220 is provided so as to be inserted within the reel hub 210. A braking gear 220A, which is annular and which can mesh with the engaging gear 216, is provided at the bottom surface of the braking member 220. The rotation restricting rib 208 of the case 202 is inserted in at the inner side of an engaging projection 222, which stands erect from the top surface of the braking member 220, such that the braking member 220 cannot rotate with respect to the case 202 but can move upward and downward. A releasing projection 223, which projects from the axially central portion of the bottom surface of the braking member 220, is disposed in the through hole 218 of the reel hub 210 and faces the gear opening 206.
A compression coil spring 224 is disposed between the braking member 220 and the ceiling plate 202B of the case 202. Usually, the braking member 220 is urged downward by the urging force of the compression coil spring 224 such that the braking gear 220A meshes with the engaging gear 216. In this way, when the recording tape cartridge 200 is not in use, it is set in a rotation locked state in which rotation of the reel 204 with respect to the case 202 is impeded. Further, the reel gear 214 is exposed from the gear opening 206 while the reel 204 is pressed toward the bottom plate 202 side of the case 202 by this urging force.
On the other hand, when the recording tape cartridge 200 is loaded into a drive device, as the driving gear 212A meshes with the reel gear 214, a releasing portion 212B, which projects from the axially central portion of the rotating shaft 212, abuts the releasing projection 223 of the braking member 220 and pushes the releasing projection 223. In this way, the braking member 220 is pushed upward against the urging force of the compression coil spring 224, and the meshing of the braking gear 220A and the engaging gear 216 is cancelled. In the state in which the driving gear 212A and the reel gear 214 are completely meshed together, the reel plate 219 of the reel 204 is attracted by the magnetic force of an annular magnet 212C provided between the driving gear 212A and the releasing portion 212B of the rotating shaft 212. The reel 204 becomes able to rotate within the case 202 while the aforementioned meshing is maintained.
Then, when the rotating shaft 212 rotates around the axial center thereof, the reel 204 rotates integrally therewith. At this time, due to the fact that the braking member 220 cannot rotate with respect to the case 202, the releasing projection 223 and the releasing portion 212B slidingly contact one another. In order to lessen the sliding contact resistance, the releasing projection 223 of the braking member 220 is formed of a resin material, and the releasing portion 212B at the drive device also is formed of a resin material.
However, the recording tape cartridge 200 having the above-described structure has the following problematic points. First, as the reel 204 rotates, the releasing projection 223 and the releasing portion 212B slidingly contact one another. Therefore, if the rotational speed of the reel 204 is high or if the period of time over which the reel 204 is rotated continuously is long, wear will occur at one or both of the releasing projection 223 and the releasing portion 212B. In this case, if wear arises at the releasing projection 223, it is possible to handle the problem by replacing the part. However, if wear arises at the releasing portion 212B at the drive device, repair is complex and the repair costs are expensive.
Secondly, because the releasing projection 223 which is relatively large projects from the bottom surface of the braking member 220, the center of gravity of the braking member 220 overall is high (a state such as a top), and when the reel 204 rotates, it may shake greatly due to the slight offset of the center thereof. Such shaking is a cause of the generation of dust due to abrasion which is caused by the abnormal contact between the engaging projection 222 and the rotation restricting rib 208, and is a cause of promoting wear of the releasing projection 223 or the releasing portion 212B. In order to prevent this, the distal end of the releasing projection 223 is formed as a flat surface 223A which planarly contacts the releasing portion 212B. However, in order to reduce the aforementioned sliding contact resistance, the surface area of the flat surface 223A is extremely small, and is insufficient to prevent the aforementioned shaking. Moreover, when the height over which the releasing projection 223 projects is low, the releasing portion 212B at the drive device must be made to be long. The relative stroke in the axial direction at the time when the reel gear 214 and the driving gear 212A mesh together is long, which is a cause of an increase in the size of the drive device.
Third, due to requirements relating to strength, durability and the like, the rotating shaft 212 is formed of a metal material. The releasing portion 212B, which is formed of a resin material in correspondence with the braking member 220 as described above, is mounted to the rotating shaft 212. Because the magnet 212C is disposed around the releasing portion 212B, the releasing portion 212B cannot be fixed from above (from the recording tape cartridge 200 side). Therefore, as illustrated, the releasing portion 212B is fixed to the rotating shaft 212 by a screw from the side of the drive source such as a motor or the like. There are therefore constraints on the layout of the motor and the like within the drive device. Namely, the degrees of freedom in the design of the drive device into which the recording tape cartridge 200 is loaded are limited.
Thus, a structure is known in which a releasing member is interposed between the braking member 220 and the rotating shaft 212. (Refer to Japanese Patent Application Laid-Open (JP-A) No. 11-185437 and Japanese Patent No. 3187022 for example.) In the structure of JP-A No. 11-185437, the releasing member is provided for the purpose of dustproofing. The releasing member is formed of a resin material, and is able to rotate relative to both the braking member and the reel. Therefore, this is not a structure which overcomes the above-described problems. On the other hand, in the structure of Japanese Patent No. 3187022, a releasing member is provided as a countermeasure to the above-described problems. Therefore, portions of this structure which differ from the recording tape cartridge 200 will be described with reference to FIGS. 12 and 13.
A recording tape cartridge 250 shown in FIG. 12 has a releasing member 252 which is disposed between the bottom portion 210A of the reel hub 210 and the braking member 220 and which is formed of a resin material. As shown in FIG. 13, the releasing member 252 is formed substantially in the shape of an equilateral triangle as seen in plan view, and has leg portions 254 projecting downward from the vertices thereof. Each leg portion 254 is inserted in an insert-through hole 256 provided in the bottom portion 210A instead of the through holes 218, and faces the gear opening 206.
The insert-through holes 256 pass through the region of the bottom portion 210A where the reel gear 214 is formed, and the diameters thereof are larger than the gear pitch of the reel gear 214. Moreover, teeth of the reel gear 214 are not provided around the insert-through holes 256. Moreover, at the top surface of the bottom portion 210A, in place of the engaging gear 216, a plurality of anchor projections 258 are provided. The anchor projections 258 are disposed at uniform intervals along a predetermined circumference which is coaxial with the reel hub 210, so as to avoid the vertices of the releasing member 252. Gear teeth 258A, which can mesh with the braking gear 220A, are formed at the top ends of the anchor projections 258.
A slide-contact projection 260 projects from the axially central portion of the top surface of the releasing member 252. The slide-contact projection 260 always abuts a slide-contact projection 262 which is provided in place of the releasing projection 223 at the braking member 220.
When this recording tape cartridge 250 is not in use, due to the braking gear 220A of the braking member 220 meshing with the gear teeth 258A of the reel 204 due to the urging force of the compression coil spring 224, rotation of the reel 204 with respect to the case 202 is impeded. In this state, the releasing member 252 abuts the braking member 220 at the slide-contact projection 260, and the bottom surface of the releasing member 252 is pressed against the bottom portion 210A. The end surfaces of the leg portions 254, which are positioned within the insert-through holes 256, are substantially flush with the addenda of the reel gear 214.
On the other hand, when the recording tape cartridge 250 is loaded into a drive device, as the reel gear 214 meshes with the driving gear 212A of the rotating shaft 212 which does not have the releasing portion 212B, the leg portions 254 are pressed by the driving gear 212A, and the releasing member 252 is pushed upward against the urging force of the compression coil spring 224. Thus, the releasing member 252, while moving away from the bottom portion 210A, pushes the braking member 220 upward, and the meshing of the braking gear 220A and the gear teeth 258A is released. In the state in which the meshing of the driving gear 212A and the reel gear 214 is maintained, the releasing member 252 holds the braking member 220 at the above-described released position, due to the leg portions 254 contacting the driving gear 212A.
Then, when the rotating shaft 212 rotates, the reel 204 rotates within the case 202. At this time, the releasing member 252, whose leg portions 254 are in the insert-through holes 256 of the reel 204, rotates integrally with the reel 204, and the slide-contact projection 260 slidingly contacts the slide-contact projection 262 of the braking member 220.
As described above, in the recording tape cartridge 250, the releasing member 252, which, at the leg portions 254 thereof, is abutting the addenda of the driving gear 212A of the rotating shaft 212, rotates integrally with the reel 204. Therefore, there are no portions at the drive device and at the recording tape cartridge 250 which slidingly contact one another as the reel 204 rotates, and there is no fear that a member at the drive device will become worn. Moreover, by interposing the releasing member 252 between the rotating shaft 212 and the braking member 220, the position of the center of gravity of the braking member 220 is lowered, and shaking of the braking member 220 at the time when the reel 204 rotates is suppressed. In particular, the releasing member 252 is pressed by the rotating shaft 212 at the leg portions 254 which are disposed so as to be separated from the axial center of the reel 204. Thus, the posture of the releasing member 252 at the time when the reel 204 rotates is stable, and it is difficult for the releasing member 252 to become a cause of shaking of the braking member 220. Moreover, because the rotating shaft 212 pushes the releasing member 252 by the driving gear 212A, there is no need to provide the releasing portion 212B which is made of resin. The structure of the recording tape cartridge 250 does not place any constraints on the layout of the motor or the like of the drive device. Note that illustration of the magnet 212C is omitted from FIG. 12.
However, even with the conventional recording tape cartridge 250 as described above, there are problems such as follows.
First, the leg portions 254 of the releasing member 252 which is made of resin are pushed by the addenda of the driving gear 212A which is made of metal, and the releasing member 252 moves the braking member 220 to a rotation permitted position and holds the braking member 220 thereat. Therefore, even if there is no sliding contact accompanying rotation at these times, wear will arise at the leg portions 254 due to use over a long period of time (i.e., repetition of the aforementioned pushing).
Second, the releasing member 252 is moved upward by the driving gear 212A which meshes with the reel gear 214. Therefore, the stroke of movement of the releasing member 252 is restricted by the height of the teeth of the reel gear 214 (the driving gear 212A), and it is difficult to ensure a releasing stroke that has leeway. In particular, when wear arises at the leg portions 254 as described above, there is the concern that the stroke of the releasing member will be reduced, and that releasing of the locking of the reel 204 will not be able to be achieved. If the leg portions 254 are made to project further than the addenda of the reel gear 214 as a countermeasure thereto, there is the concern that the locking of the reel 204 will be released when the recording tape cartridge 250 is not in use.
Third, usually, the reel gear 214 is formed on the whole in the shape of a ring having a large diameter, in order to make the driving force from the rotating shaft 212 small. Namely, at the bottom portion 210A, the reel gear 214 is disposed as far as possible from the axial center. On the other hand, in order to ensure the braking force of the braking member 220, the anchor projections 258 having the gear teeth 258A are disposed on a circumference which has as large of a diameter as possible. Namely, the reel gear 214 and the anchor projections 258 are disposed at substantially the same position in the vertical direction, or the reel gear 214, which is formed at the outer surface side, is disposed slightly further toward the radial direction outer side than the anchor projections 258. Therefore, in order for the anchor projections 258 to not interfere with the vertices of the releasing member 252 (portions corresponding to the region where the reel gear 214 is formed), the anchor projections 258 cannot be provided continuously in the form of a ring. Accordingly, the anchor projections 258 must be provided at discrete positions. As compared with the above-described engaging gear 216 which is provided in an annular form, the centering function (centripetal force) of the braking member 220 due to the meshing is weak. Due to the centering function being weak, at the recording tape cartridge 250, it is easy for the braking member 220 to ride up on the gear teeth 258A in particular at the time of assembling the braking member 220, and careful work (in an automatic assembling device, high-level monitoring) is required. Moreover, at the reel gear 214 as well, similarly, the insert-through holes 256 are not continuous in the peripheral direction. Therefore, the centering function is weak, and the torque which can be transmitted from the rotating shaft 212 is small.
Fourth, because the releasing member 252 is disposed within the reel hub 210, the rotation locked position of the braking member 220, which is disposed so as to be separated from the bottom portion 210A, is higher by an amount corresponding to the thickness of the releasing member 252, and there is the possibility that the braking of the reel 204 by the braking member 220 will not be stable. Further, because the rotation locked position is high, the height by which the anchor projections 258 project from the bottom portion 210A is high as compared with the engaging gear 216, and thick portions are formed at the reel hub 210. In this way, the flowability of the resin at the time of molding the reel hub 210, which is formed by usual resin molding, is poor, which is a cause of deterioration of the moldability.
As described above, there is still room for improving a releasing member for releasing the state in which a reel is locked by a braking member.